Sockets are used widely in the electronics industry to mount and connect microelectronic devices such as semiconductor integrated circuits (“ICs”) to electronics systems of various sorts—as is well known, a socket is used to connect terminals on a device to corresponding contacts on a printed circuit board or other electrical interconnection means. In addition, sockets are routinely used in systems for: (a) testing electronic device performance (an assortment of socket types have been developed to connect to a device under test (“DUT”) having a wide variety of terminals and configurations); or (b) burn-in of electronic devices at elevated temperatures.
Prior art sockets are differentiated typically according to device terminals and intended end use (i.e., application). As such, sockets are typically designed to make electrical contact to microelectronic devices having specific types of device terminals—types of device terminals contacted by sockets include pin grid arrays (“PGAs”), J-leads, gull-wing leads, dual in-line (“DIP”) leads, ball grid arrays (“BGAs”), column grid arrays (“CGAs”), flat metal pads (“LAN” grid arrays or “LGAs”), and many others. Many contactor technologies have been developed to provide sockets for microelectronic devices with this variety of terminals. In addition to the foregoing, further differentiation among prior art sockets refers to low insertion force (“LIF”) sockets, zero insertion force (“ZIF”) sockets, auto-load sockets, burn-in sockets, high performance test sockets, and production sockets (i.e., sockets for use in products). In further addition to the foregoing, low cost prior art sockets for burn-in and product applications typically incorporate contactors of stamped and formed springs to contact terminals on a DUT. In still further addition to the foregoing, for high pin-count prior art sockets, a cam is often used to urge device terminals laterally against corresponding contactors to make good contact to each spring while allowing a low or zero insertion force.
For specialized applications, prior art sockets have used a wide variety of contactors, including anisotropic conductive sheets, flat springs, lithographically formed springs, fuzz buttons (available from Cinch, Inc. of Lombard, Ill.), spring wires, barrel connectors, twisted wire springs in an elastomer, and spring forks, among others. Prior art sockets intended for applications where many test mating cycles (also referred to as socket mount-demount cycles) are required typically use spring pin contactors of the type exemplified by Pogo® spring contacts (available from Everett Charles Technologies of Pomona, Calif.). Spring probes for applications in the electronics test industry are available in many configurations, including simple pins and coaxially grounded pins. Most prior art spring probes consist of a helical wire spring disposed between a top post (for contacting terminals on the DUT) and a bottom post (for contacting contacts on a circuit board—a device under test board or “DUT board”).
Prior art sockets typically consist of a plurality of contactors disposed in an array of apertures formed through a dielectric holder. By way of example, a high performance, prior art test socket may incorporate a plurality of Pogo® spring contacts, each of which is held in a pin holder consisting of an array of holes through a thin dielectric plate. The dielectric material in a high performance, prior art test socket is typically selected from a group of dimensionally stable polymer materials including: glass reinforced Torlon 5530 available from Quadrant Engineering Plastic Products, Inc. of Reading, Pa.; Vespel; Ultem 2000 available from GE Company GE Plastics of Pittsfield, Mass.; PEEK; liquid crystal polymer; and others. The individual Pogo® spring contacts are typically selected and designed for signal conduction at an impedance level of approximately fifty (50) ohms. In certain high performance, prior art configurations, the contactor is a coaxial type having a center spring pin with a contactor barrel body enclosed within a cylindrical, coaxial, ground shield spaced to achieve a desired signal impedance, typically fifty (50) ohms.
Materials other than the above-identified dielectric sheets have been used for prior art socket bodies. For example, ceramic materials including alumina, aluminum nitride, and low temperature co-fired ceramic are used for high temperatures. In addition, insulation coated, metal socket bodies have been used to control dimensional stability over a range of temperature. In further addition, laminated bodies of alternating layers of dielectric and metal materials in thermal contact with elastomeric contactors and compliant contactors have been used. Alignment of the contactors of a socket to the mating terminals of a DUT is an important function of a socket, particularly when the ambient temperature of the socket and mated DUT is changed over a wide range, which in modern usage may cover a range from −55° C. to +150° C.
Advances in ICs have resulted in devices with an increasing number of contact terminals, where the spacing between terminals continues to decrease. At present, terminals on packaged ICs have a minimum spacing on the order of 0.4 mm, where terminal density is projected to progress continually to smaller spacing and finer pitch. Advanced IC devices are typically tested in parallel, where several DUTs are tested simultaneously. DUTs are tested in parallel by an automatic handling system that inserts a number of devices into a corresponding array of sockets, at one time. Driven by demands for higher test efficiency, the number of DUTs tested in parallel is increasing from 8 in parallel to 16, 32 or more in the future. Advances in test technology result in smaller contact spacing, more parallel testing and wider ranges of test temperatures. These advances require more accurate alignment of arrays of sockets suited to contacting fine pitch DUTs over a wide temperature range.
In light of the above, despite the many socket technologies available in the prior art, there is a need for a socket that can resolve one or more of the above-identified issues relating to alignment accuracy of the socket to the mating DUT, and particularly to alignment of arrays of fine pitch DUTS to a mating array of sockets, where alignment must be held over a wide range of ambient temperatures.